Researchers at the Advanced Technology Institute at the University of Surrey in the UK along with more than 100 collaborators, including Prof. Vincenzo Pecunia at Simon Fraser University in British Columbia examined a range of materials to put together a roadmap for sustainable materials for energy harvesting systems. These materials included solar cells, materials for thermal energy and even RF energy capture.
Compact energy harvesters will be essential for supplying the Internet of Things ecosystem of smart gadgets, which is rapidly expanding and includes anything from smart homes and cities to smart manufacturing and smart healthcare. Using a variety of physical mechanisms, including the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and electromagnetic power transmission, efficient conversion of ambient energy into electricity is required.
It is difficult to determine how to make energy-harvesting materials sustainably. One explanation for this is the variety of parts that make up harvesters, including transducers, power management, and energy storage.
The 225-page roadmap discusses the current status of research into different classes of materials being produced for solar, piezoelectric, triboelectric, thermoelectric, and radiofrequency energy collection, as well as the environmental impact.
The difficulty of synthesizing materials that are effective for maximal energy conversion and environmentally safe is one of the main challenges of sustainability of energy harvesting materials. The manufacturing process is not always guaranteed to be sustainable when such resources are required.
Yet, it is crucial to assess the environmental impact of energy harvesting materials and technologies during the design or pilot stage before making costly commitments of resources. These analyses can help in communicating important findings to those in charge of developing educational materials and making policies.
The availability of appropriate materials for systems to transform ambient energy into usable electric energy is crucial for energy harvesting. The study of energy harvesting capabilities, the engineering of novel material discoveries' compositions, microstructures, and processing, as well as their integration into systems and devices, all require extensive, cross-cutting research.
The minimal power density offered by ambient energy sources presents a significant problem for all energy harvesting systems, necessitating the development of energy harvesting materials and equipment that can effectively convert such energy. When harvesting ambient energy, current energy harvesting devices typically produce electric power densities much below the mW cm-2.
Organic, dye-sensitized, colloidal quantum dot, and perovskite solar cells (PSCs), among other innovative solar photovoltaic materials, have recently come into the spotlight and have been hailed as environmentally and economically feasible alternatives to conventional silicon-based technology. This claim has been supported by numerous LCA studies that compared two PSC types to other solar kinds across sixteen impact categories, with the results showing that the PSC not only displayed an environmental advantage but also had a short energy payback period. Due to the removal of processing for silicon and rare earth elements, there has been a reduction in the energy-intensive operations necessary for PSC manufacture.
Unfortunately, due to the substantial amount of energy needed to produce gold from its ore, its usage in the PSC material architecture had a negative environmental impact. Further LCA research is needed in the context of ambient energy harvesting for IoT applications.
The use of lead in piezoelectric materials has been forbidden due to the toxicity of the materials and international policy efforts and regulations like the Waste Electrical and Electronic Equipment (WEEE) and Restriction of Hazardous Substances (RoHS). This has rekindled the competition to create lead-free substitutes for lead zirconate titanate based on potassium sodium niobate (KNN) and sodium bismuth titanate (NBT) (PZT).
The LCA demonstrated that KNN is environmentally worse than PZT with respect to climate change and eco-toxicity because it contains niobium pentoxide, whose mining and milling through hydro- and pyro-metallurgical processing for niobium refining has significant negative effects across a wide range of environmental indicators.
In contrast to PZT and KNN, NBT used less energy during synthesis, resulting in a lower overall environmental profile based on primary energy use and toxicological impact. NBT has a higher environmental impact than PZT when compared to lead oxide because it requires more processing and refining, which increases the difficulty of metallurgical recovery.
Triboelectric nanogenerators (TENGs) have the ability to produce energy in inexpensive self-powered devices, however, it is unknown how they will affect the environment. An LCA and techno-economic analysis of two TENG modules compared Module A, which uses a planar structure based on electrodes generating periodically charged triboelectric potential to produce energy from water and airflow as well as the movement of the body, with Module B, which uses a thin-film-based micro-grating TENG with its electrode arrays arranged linearly to generate enough energy to power standard electronics. According to the findings, Module A has a superior environmental profile, cheaper production costs, less CO2 emissions, and a quicker payback period for energy (EPBP).
Due to its higher structure's acrylic content and higher electrical energy needs during production, Module B has a higher environmental impact. Nonetheless, acrylic can be reused or recycled at the end of its useful life and does not emit any hazardous gases when burned, which enhances its overall profile. Although Module B is slightly more expensive than a PV technology based on methyl ammonium lead iodide perovskite structures, TENG modules nevertheless offer a better environmental profile and quicker payback period when compared to developing solar PV materials technologies. The identification of less expensive materials and production techniques will not be as significant as future work on TENG on lifetime and efficiency improvements.
This is due to the fact that ambient energy harvesters may have significant embodied energy (i.e., emissions along all value chains). The net environmental benefit would therefore be a more appropriate measure of worth because it compares the embedded energy to the operational energy saved over the course of their lives as well as the energy that would otherwise be needed if, for example, batteries were used as the power source.
Because the constituent minerals contain heavy metals and rare-earth elements, more focus has been placed on their toxicity and less on the environmental profile of their supply chains.
The inorganic variety produced much greater environmental impacts, according to a comparison of the lifetime effects of inorganic, organic, and hybrid thermoelectric materials at their production stage across numerous environmental indices. Bi2Te3 was found to be the sole inorganic exception with the least negative environmental impact of all the thermoelectric materials examined. Risks associated with the raw material supply were highlighted as the primary sustainability issue for organic and hybrid varieties.
Click here to read 'Roadmap on Energy Harvesting materials".
